This disclosure is directed to charts to be mounted on a chart drive. A chart drive is a mechanism which rotates a chart to enable a variable quantity dependent on time to be marked on the chart. One chart drive is described in U.S. Pat. No. 2,978,287. In all probability, there are tens of thousands of chart drive mechanisms already installed. A typical chart drive installation includes a motor which rotates a chart adjacent to a marking instrument such as a self-inking pen. The pen, itself, is connected on some kind of movable apparatus, and its position is controlled by a transducer. The transducer measures some quantity of interest.
One typical setting where a chart drive mechanism is utilized is in the measurement of natural gas flowing through a pipeline. Natural gas is sold by applying the actual gas delivered through a pipeline to a norm or standard measure. The standard measure presumes a fixed volume of gas at a specific pressure and specific temperature. In fact, the flow rate of natural gas in a pipeline is highly variant. Also, the temperature of the gas is variant. Therefore, specific knowledge of the flow rate and temperature is required to determine the amount of gas that has been delivered for a given interval. Since flow rate and temperature are dynamic variables, it is necessary to measure both variables and chart them over the time interval of interest. The charting is typically accomplished with a chart drive mechanism of the sort mentioned above.
In most instances, a chart drive recorder mechanism is located at a place where daily service is not ordinarily convenient. Typically, such an apparatus is equipped with more than one chart, the charts being stacked and mounted on a support or backing which is a circular disk. The charts which are mounted on the disk are supported adjacent to the writing instrument so that it can form a mark on every chart. As the mark is made, the chart records the data of interest. Typically, a chart will record data for twenty-four hours. The chart drive mechanism includes a chart ejection mechanism. This device separates the topmost chart (the one having data for the past 24 hours already marked on it) and causes it to be dropped below the equipment into a storage hopper. This then exposes the next chart of the stack. The next chart is then used for recording during the next time interval. This process is repeated indefinitely. Typically, a chart drive mechanism will be installed with a number of charts stacked on it. The charts are actually identical to one another and differ only in that they are used to record different data. A typical installation may require placing fourteen charts on a chart drive mechanism so that data can then be recorded for two weeks.
A typical chart drive installation includes a storage hopper where previously marked and dropped charts are received and stacked. When the equipment is serviced, the charts are removed and carried away for subsequent conversion into data representative of the natural gas which has flowed through the pipeline. Through the use of formulas not relevant, the actual price for natural gas can be calculated and is adjusted to a norm.
Many times, recording chart installations are found in inclement environments. They may be located in coastal or swamp areas and are, therefore, exposed to high humidity levels. They are also installed in very remote locations as, for example, in a locale exposed to extreme cold and inclement weather. If is for this reason that they sometimes cannot be serviced on a daily basis.
It is required of a chart drive mechanism that it run accurately so that accurate measurements can be taken of the data and applied to the price calculation formulas. Indeed, it is not unusual for a chart drive mechanism to be installed on a natural gas pipeline for making measurements to be applied through a formula in the sale of $100,000 worth of gas daily. Clearly, it is essential that the chart drive mechanism operate reliably.